1. Technical Field
The present invention relates to a focus control method and a culture observation apparatus, and more particularly to a focus control method and a culture observation apparatus that can suitably be used for observing a subject floating in a culture medium drop.
2. Background Art
A focus control method of the present invention is a focus control method for detecting a focusing position of a subject in a culture container, this method including: an area specification step of specifying a detection area which includes a subject in the culture container; an AF area setting step of selecting and setting an AF area, which does not include an area located within a predetermined distance from an edge of the culture container and includes a boundary portion of the subject, out of the detection area; and a focal position detection step of detecting, by a focal position detection unit, a focusing position on the subject in the AF area.
A culture observation apparatus of the present invention is a culture observation apparatus having a microscope for observing a transparent culture container in which a culture medium drop is disposed, this apparatus having: an objective lens of the microscope; an observation unit for imaging the culture medium drop via the objective lens and generating an observation image; a specification operation unit for specifying a detection area which includes the culture medium drop in the culture container; an area setting unit for selecting an AF area, which does not include an area located within a predetermined distance from an edge of the culture container and includes a boundary portion of the culture medium drop, out of the detection area; and a focal position detection unit for detecting a focusing position on the culture medium drop in the AF area.
In the cell culture system however, it is difficult to detect a focusing position on the cells without operation of the observer, so in the cell culture system often the objective lens is moved based on the focal position specified by the observer in advance, and a plurality of observation images is captured. In other words, in the cell culture system, the objective lens is moved along the optical axis thereof from the specified focal position as the center, and observation images are captured at each position of the objective lens.
This is based on the assumption that if the observer specifies a position of the objective lens to be focused on the cells, as the focal position, and if the objective lens is moved to each position from this focal position as the center to capture observation images, then an observation image focused on the cells should be obtained.
Patent Document 1: Japanese Patent Application Laid-Open No. 2007-6841
In the case when an observation surface of the observation target in the cell culture system is relatively stable, such as a case of an adhesive cell, it is highly possible to obtain an observation image focusing on the cell, if a plurality of observation images is captured while moving the position of the objective lens. However in the case when the observation target is a floating cell, it may be difficult to obtain an observation image focused on the cell, even if a plurality of observation images is captured while moving the position of the objective lens.
For example, in a clinic where external fertilization is performed, a culture medium drop may be disposed on a dish, and a fertilized embryo may be cultured in the culture medium drop. In such a case, the fertilized embryo freely moves in the culture medium drop, hence it is impossible to specify in advance a position of the objective lens at which the fertilized embryo enters the observation field of view, and at which the fertilized embryo is focused. Therefore in the cell culture system, it has been difficult to automatically observe a fertilized embryo without operation of the observer.
Particularly if the culture medium drop is near the edge of the dish, illumination unevenness is generated since light is eclipsed on the side wall face of the dish, hence it is difficult to detect a position of the objective lens where the fertilized embryo is focused on.